The present invention relates generally to spectral estimation of radar time-of-arrival periodicities, or more particularly to a method to extract the periodic properties (or Pulse Repetition Intervals (PRIs)) of radar signals whose time-of-arrival at an airborne platform have been time tagged by an Electronic Warfare (EW) receiver.
An EW receiver time tags the arrival of radar pulses to extract the Pulse Repetition Interval. If the receiver is exposed to a single radar signal which is stable in time as in FIG. 1, the PRI is easily calculated by taking the time difference between successive time-of-arrival samples. In practice, many radar pulse trains are interleaved in time and each individual pulse train may be staggered or jittered in time. Under these conditions the simple time-difference-of-arrival (TDOA) scheme presented above fails to give the correct PRIs. In this case a more complicated time domain deinterleaving scheme must be employed. The periodogram spectral estimator which is computed by taking the modulus of the Discrete Fourier Transform (DFT) of time series data is a simple and efficient method for revealing periodicities. The following U. S. Pat. Nos. are of interest.
3,955,200--Miller PA1 4,394,642--Currie et al PA1 4,516,220--Baumann PA1 4,518,947--Poston et al PA1 4,568,915--Gutleber PA1 4,721,958--Jenkin PA1 4,879,561--Inkol PA1 4,918,455--Maier PA1 5,056,105--Darmon et al PA1 5,063,385--Caschera PA1 5,115,246--Thomas, Jr. et al
Baumann discloses a pulse deinterleaving signal processor and method wherein the spectral signature of different pulses are stored in target files, and the time interval between pulses is calculated from the time of arrival of each pulse. The time interval between pulses from a common source can be determined through use of the processor.
Jenkin discloses a real-time pulse processor utilizing a folded shift register to perform the deinterleaving. The interpulse pulse repetition (PRI) is determined for use in identifying an emitter. The apparatus first deinterleaves a signal that comprises a plurality of interleaved pulse trains into its constituent pulse trains, and then identifies the emitter which transmitted each pulse train.
Inkol discloses a filter system for radar applications which permits observed data measurements for a multiplicity of radar emitters to be deinterleaved and stored in a buffer memory. It allows data corresponding to any one of the radar emitters to be accessed for further analysis.
Maier discloses an associative hierarchial deinterleaver which generates its own models based on the signals received. It groups signal pulses which have at least one similar parameter; it predicts a value for a different parameter for other signal pulses which have yet to be associated with the group; it associates similar signals depending on parameters; and it reports an indication of the parameters of the group after a threshold number of pulses is associated with the group.
Darmon et al disclose an interleaving method for a digital transmission system where deinterleaving is performed symmetrically by means of an inverse pilot sequence suitable for reconstituting successive code words.
Caschera discloses a radar warning receiver compressed memory histogrammer for initial processing of the received data for quickly determining the numbers and types of emitters in a system's environment.
The remaining references are for general background material.